Alzheimer's disease is a progressive, degenerative disease of the brain, which causes thinking and memory to become seriously impaired. It is the most common form of dementia.

Alzheimer's is characterized by "plaques"- numerous tiny deposits scattered throughout the brain which become toxic to brain cells at excessive levels; and "tangles" which interfere with vital processes eventually choking off the living cells. As well, when brain cells degenerate and die, the brain markedly shrinks in some regions. As Alzheimer's progresses and affects different areas of the brain, various abilities become impaired. The result is changes in abilities and/or behaviour. At present, once an ability is lost, it is not known to return. Research, however, is now suggesting that some relearning may be possible.